This invention relates generally to techniques for making measurements along telephone circuits and, more specifically to techniques for making such measurements in order to determine the effects of a telephone circuit on dial pulse signals.
In communication networks, it is necessary to establish connection between two different points and this is usually done through an addressing system. In the typical telephone system, dial pulses or dial tones are used to signal to the nearest telephone office a request for connection of the initiating telephone to the address indicated by the number and configuration of pulses or tones. This address information must be passed on (repeated) to the next involved central office until the connection to the addressed telephone is established.
Monitoring and measuring the performance of this addressing portion of the telephone system is important. Many instruments exist for making measurements on telephone lines that utilize the dial-pulse method of signaling. To obtain accurate measurements, most of the available instruments require breaking the circuit and terminating it with the measuring instrument. One of the parameters these instruments generally attempt to measure is the percent break of the pulsing device. However, many of these instruments cannot accurately measure percent break when the pulse waveform is distorted by the characteristics of the measured circuit. A number of features not found in these instruments would be very desirable to improve the usefulness of the measuring equipment. One feature is to be able to make measurements of the dial characteristics without having to break the circuit. Another feature enables the instrument to perform a measurement on the circuit itself without modifying dial pulse characteristics of the circuit. Another very desirable characteristic is to be able to bridge across the circuit and obtain measurements not only at specific points, but virtually at any point along the circuit wherever access could be obtained. Yet another desireable characteristic is the ability to accurately measure the percent break of the pulsing device despite the presence of substantial amounts of inductance and capacitance in the measured circuit. It is a principal object of the present invention to provide a method and apparatus for making dial pulse signaling circuit measurements with these features and characteristics.
One commercially available technique that has some of these desirable characteristics provides a circuit that processes the voltage pulse by compression and delay in a complex circuit. It is another object of the present invention to provide a circuit with all of the above desirable characteristics that is simple, inexpensive and easy to use.